Re: adding noise to an image

[Paul Davis <pjdavis engineering uiowa edu>]

Amadeus W.M. wrote:

> Thanks for the answer! I know about noise, I do computer vision for a
> living. I wasn't sure how to draw it. I guess there's no way around
> having e.g. a 
>
> vector<Gdk::Color> gray(256);
> Glib::RefPtr<Gdk::Colormap> cmap = Gdk::Colormap::get_system(); // e.g.
>
> for(int i=0; i<gray.size(); i++)
> 	gray[i].set_grey_p(i/256.0*100);
>
> cmap->allocate_colors(gray, ... ); // do I need to allocate them?
>
>
> Anyway, it's not very easy to have a pixbuf with shapes drawn on it, and
> noise. You run into all sorts of unpleasant interactions, so I decided
> to make a separate application for noise, after no more shapes are being
> drawn. 
>
> Thanks again.
>
>
>  
>
> > For an explanation of noise, take a look at this:
> > http://www.icaen.uiowa.edu/~dip/LECTURE/ImageProperties3.html#noise
> >
> > Decide on a value for sigma and then use the slider to change this 
> > value.  I'd have to take a look at how you draw your image to be sure on 
> > the best way to add this.  Generally, you should look at adding it to 
> > your pixmap before drawing it with whichever drawing function you use.
> >
> > Good luck
> > Paul
> >    
>
>  
lol, well I bet you do know about noise then.

A thought just occurred to me.  An easy way to do this would be draw the 
shapes by hand.  Then you could just add noise at the end to your image 
data.

Might be a bit inefficient having two copies of the image around( the 
original and the noisy ).  But drawing the shapes and the noise could be 
done failry simply.

img = get_original_img() ;

for( int y = 0 ; y < img_height ; y++ )
{
   for( int x = 0 ; x < img_width ; x++ )
   {
         if( on_shape_border( x, y )
         {
            img[ y * img_width + x ] = border_val ;
         }

         image[ y * img_width + x ] = get_noised_val( x, y )
   }
}

draw resulting image to drawing area.

Just a thought.

Cheers,
Paul